Strong Interface Coupling Enables Stability of Amorphous Meta‐Stable State in CoS/Ni 3 S 2 for Efficient Oxygen Evolution

Abstract Rational design of heterostructure catalysts through phase engineering strategy plays a critical role in heightening the electrocatalytic performance of catalysts. Herein, a novel amorphous/crystalline (a/c) heterostructure (a‐CoS/Ni 3 S 2 ) is manufactured by a facile hydrothermal sulfurization method. Strikingly, the interface coupling between amorphous phase (a‐CoS) and crystalline phase (Ni 3 S 2 ) in a‐CoS/Ni 3 S 2 is much stronger than that between crystalline phase (c‐CoS) and crystalline phase (Ni 3 S 2 ) in crystalline/crystalline (c/c) heterostructure (c‐CoS/Ni 3 S 2 ) as control sample, which makes the meta‐stable amorphous structure more stable. Meanwhile, a‐CoS/Ni 3 S 2 has more S vacancies (S v ) than c‐CoS/Ni 3 S 2 because of the presence of an amorphous phase. Eventually, for the oxygen evolution reaction (OER), the a‐CoS/Ni 3 S 2 exhibits a significantly lower overpotential of 192 mV at 10 mA cm −2 compared to the c‐CoS/Ni 3 S 2 (242 mV). An exceptionally low cell voltage of 1.51 V is required to achieve a current density of 50 mA cm −2 for overall water splitting in the assembled cell (a‐CoS/Ni 3 S 2 || Pt/C). Theoretical calculations reveal that more charges transfer from a‐CoS to Ni 3 S 2 in a‐CoS/Ni 3 S 2 than in c‐CoS/Ni 3 S 2 , which promotes the enhancement of OER activity. This work will bring into play a fabrication strategy of a/c catalysts and the understanding of the catalytic mechanism of a/c heterostructures.